Tentative implementation of string slices (hidden under the flag --string-slices).

src/objects-debug.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 331 matching lines @@
   VerifyObjectField(kStackFramesOffset);
 }
 
 
 void String::StringVerify() {
   CHECK(IsString());
   CHECK(length() >= 0 && length() <= Smi::kMaxValue);
   if (IsSymbol()) {
     CHECK(!HEAP->InNewSpace(this));
   }
+  if (IsConsString()) {
+    ConsString::cast(this)->ConsStringVerify();
+  } else if (IsSlicedString()) {
+    SlicedString::cast(this)->SlicedStringVerify();
+  }
 }
 
 
+void ConsString::ConsStringVerify() {
+  CHECK(this->first()->IsString());
+  CHECK(this->second() == GetHeap()->empty_string() ||
+        this->second()->IsString());
+  if (this->IsFlat()) {
+    // A flat cons can only have a sequential string as first part because only
+    // String::SlowTryFlatten can convert a cons into a flat cons.
+    CHECK(this->first()->IsSeqString());
+  }
+}
+
+
+void SlicedString::SlicedStringVerify() {
+  CHECK(!this->parent()->IsConsString());
+  CHECK(!this->parent()->IsSlicedString());
+  if (this->IsTruncated()) {
+    CHECK(this->offset() == 0);
+    // A truncated slice cannot have an external string as parent because only
+    // String::SlowTryTruncate can convert a slice into a truncated slice.
+    // There is no way to gain direct access to the truncated parent string,
+    // therefore the truncated parent cannot be morphed into an external string.
+    CHECK(this->parent()->IsSeqString());
+  }
+}
+
+
 void JSFunction::JSFunctionVerify() {
   CHECK(IsJSFunction());
   VerifyObjectField(kPrototypeOrInitialMapOffset);
   VerifyObjectField(kNextFunctionLinkOffset);
   CHECK(next_function_link()->IsUndefined() ||
         next_function_link()->IsJSFunction());
 }
 
 
 void SharedFunctionInfo::SharedFunctionInfoVerify() {
@@ skipping 395 matching lines @@
         ASSERT(e->IsUndefined());
       }
     }
   }
 }
 
 
 #endif  // DEBUG
 
 } }  // namespace v8::internal